U.S. patent application Ser. No. 322,348, which is incorporated herein for purposes of reference, discloses several patents, each of which teaches the imposition of means to isolate the compartment power receivers upon removing the circuit breaker from the compartment. The aforementioned U.S. patent application utilizes a balanced arrangement of shutter linkage mechanisms on both sides of the unit to prevent manual operation by an operator in any attempt to bypass the shield unit. The present invention distinguishes over the aforementioned U.S. patent application by employing "roller-line" mechanism on both sides of the breaker compartment to prevent manual operation of the shield unit when the breaker is removed from the compartment.